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Groups > comp.lang.prolog > #14842

unify_with_occurs_check/2 might have been fixed (Was: Scryer Prolog unify_with_occurs_check/2 doesn't scale)

From Mild Shock <janburse@fastmail.fm>
Newsgroups comp.lang.prolog
Subject unify_with_occurs_check/2 might have been fixed (Was: Scryer Prolog unify_with_occurs_check/2 doesn't scale)
Date 2025-09-25 01:50 +0200
Message-ID <10b2038$1ce0$1@solani.org> (permalink)
References <107t0fi$6bgl$1@solani.org> <10ajo4u$k5kc$1@solani.org>

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Hi,

Scryer Prologs unify_with_occurs_check/2 might have
been fixed. I can now test the following:

/* Scryer Prolog 0.9.4-660 */

% ?- bench, bench, bench.
% [...]
%    % CPU time: 0.148s, 57 inferences
%    % CPU time: 0.126s, 57 inferences
%    % CPU time: 0.214s, 58 inferences
%    % CPU time: 0.213s, 58 inferences
%    true.

% ?- bench2, bench2, bench2.
% [...]
%    % CPU time: 0.036s, 58 inferences
%    % CPU time: 0.042s, 58 inferences
%    % CPU time: 0.018s, 59 inferences
%    % CPU time: 0.096s, 56 inferences
%    true.

This was the test case, it includes
unify_with_occurs_check/2:

hydra(0, _) :- !.
hydra(N, h(X, X)) :- N > 0, N0 is N-1, hydra(N0, X).

hydra(0, A, A) :- !.
hydra(N, h(X, X), A) :- N > 0, N0 is N-1, hydra(N0, X, A).

bench :-
    hydra(1048576, X), hydra(1048576, Y, Y),
    time(X = Y),
    time(unify_with_occurs_check(X, Y)),
    time(X == Y),
    time(compare(_, X, Y)), fail; true.

bench2 :-
    hydra(1048576, X), hydra(1048576, Y, Y),
    time(copy_term(X-Y,_)),
    time(term_variables(X-Y,_)),
    time(\+ ground(X-Y)),
    time(acyclic_term(X-Y)),
    fail; true.

Bye

Mild Shock schrieb:
> Hi,
> 
> Since some idiots blocked me on Scryer Prolog issues,
> I raise the issue here. Basically uniy_with_occurs_check/2
> probably does use a different implementation of unification
> 
> than find for (=)/2. Because it doesn't scale, I find:
> 
> /* Scryer Prolog */
> ?- test3(25).
>     % CPU time: 0.001s, 57 inferences
>     true.
> 
> ?- test4(25).
>     % CPU time: 2.133s, 57 inferences
>     true.
> 
> Expectation would be that unify_with_occurs_check/2
> does just scale like it does in SWI-Prolog. In
> SWI-Prolog I find:
> 
> /* SWI-Prolog 9.3.30 */
> ?- test3(25).
> % -1 inferences, 0.000 CPU in 0.000 seconds (0% CPU, Infinite Lips)
> true.
> 
> ?- test4(25).
> % -1 inferences, 0.000 CPU in 0.000 seconds (0% CPU, Infinite Lips)
> true.
> 
> The test case was simply a hydra variant. Actually the
> last hydra modification posted by @kuniaki, which I
> am currently ticking along now:
> 
> hydra(0, _) :- !.
> hydra(N, h(X, X)):- N>0, N0 is N-1, hydra(N0, X).
> 
> hydra(0, A, A) :- !.
> hydra(N, h(X, X), A):- N>0, N0 is N-1, hydra(N0, X, A).
> 
> test3(N) :- hydra(N, X), hydra(N, Y, Y),
>     time(X = Y).
> 
> test4(N) :- hydra(N, X), hydra(N, Y, Y),
>     time(unify_with_occurs_check(X, Y)).
> 
> But of course there is a cut (!) in the first rules.
> 
> Mild Shock schrieb:
>> Hi,
>>
>> WebPL is already outdated I guess. It doesn't
>> show the versions of the other Prolog systems
>> it is using. While I had these results for
>>
>> the primes example in the WebPL playground:
>>
>> /* Trealla Prolog WASM */
>> (23568.9ms)
>>
>> When I run the example here:
>>
>> https://php.energy/trealla.html
>>
>> I get better results:
>>
>> /* trealla-js 0.27.1 */
>>
>> ?- time(test).
>> % Time elapsed 9.907s, 11263917 Inferences, 1.137 MLips
>>
>> Bye
> 

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Thread

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